Hello,

This schematic diagram is for a "light controlled bird" project from Maxitronic 500 in 1. I'm having trouble determining the type and rating for both the transformer and the corresponding speaker? I've checked the manual it does not say what type except its a OPT/Power Transformer and a speaker which converts electrical energy into sound energy.

Pcflyf77

 

This Circuit must be fairly old,
I haven't seen a Schematic for a Transistor Amp with an Audio-Output-Transformer in ~40 years.

Audio-Output-Transformers are normally only seen in Tube-Amps now.

It's not likely that You will find an exact replacement Transformer anywhere.
.
.
.

 

Go find an old transistor radio with an audio output transformer and try that transformer.

Your best bet will probably be with radios made before about 1990,

 

This Circuit must be fairly old

positive earth, no less.

 

Yes- this type of transformer is all but obsolete in this modern world.

It would be a ~ 1K to 8 ohm type of output transformer typically found in old transistor radios.
This would be an approximate turns ratio of 25:1

 

 

These things and many other types where at the 99 cent store. Not now.

 

It's not likely that You will find an exact replacement Transformer anywhere.

Mouser has a large selection of small output transformers, with over 29,000 pieces in stock or on order. Digi-Key also has some, but Mouser has more.

ak

 

The circuit is a variation of a circuit in the old GE transistor manual, back when PNP's ruled the day.

ak

 

this type of transformer is all but obsolete in this modern world.

Disagree. Mouser has over 29,000 in stock or on order, for a reason.

It would be a ~ 1K to 8 ohm type of output transformer typically found in old transistor radios. This would be an approximate turns ratio of 25:1

Maybe not. This:

I've checked the manual it does not say what type except its a OPT/Power Transformer

might be a clue. Often these kinds of project kits have relatively few electronic components, each one doing 17 things. The transformer could be a small, custom made part good for both AC power projects and audio output. Wouldn't be surprised. If I were buying one, I'd start with a 500CT:8CT, 500 mW to 1 W, to get the most options out of one part.

ak

 

These things where at the 99cent store. Not now.

 

I believe without knowing that you need a1KΩ -8Ω audio transformer, they used to be common as dirt, but not so much now.

 

I thought that circuit looked familiar. I have this saved from over 10 years ago.


This is almost identical to the circuit in post #1; definitely the same concept.

Updated with an NPN transistor
Some component value differences
No thermistor

Here is the site: http://www.radiolocman.com/shem/schematics.html?di=62835

Here is the audio: http://www.rlocman.ru/i/Media/2010/29/bird.wav

Here is the text:

This circuit is a modified hartley oscillator with a couple of extra components included. The transformer is a small audio transformer, type LT700. The primary is center tapped with an impedance of 1Kohms at 1KHz . The secondary has an impedance of 8 ohms. The inclusion of R1 and C1 give this oscillator its characteristic "chirp". As the 100u capacitor charges via the 4.7K resistor, R1 the bias for the transistor is cut off. This causes the oscillation to stop, the capacitor discharges through the base emitter circuit of the transistor and oscillations start again. Altering these components alters the frequency of the chirp. The chirp is also voltage dependent. When the push button switch is operated the 100u capacitor is charged. When its released, the oscillation decays and the chirp becomes faster.

ak

 

Here is the schematic from post #1, re-drawn for clarity. You can see the similarities between it and the newer circuits.

We don't know the value of the CdS cell or the part number for the transistor. 2N404 was a very popular type back in that day.

Yes, the battery looks upside-down. This shows the overall form of the circuit in a way more people are familiar with.

ak

 

positive earth, no less.

"Positive Earth"???? There is no ground connection shown, and none would provide any benefit at all. PNP circuits did, unfortunately, tend towards positive commons.
And the transformer could indeed come from most small transistor radios from the sixties or seventies.

 

Reminds me of a circuit I saw in a 50 in 1 kit I got in the mid 70's as a kid. I wish I had the handbook of circuits I had back then.

 

Reminds me of a circuit I saw in a 50 in 1 kit I got in the mid 70's as a kid.

It probably is the same circuit. A lot of those kits "shared" ideas.

ak

 

PNP circuits did, unfortunately, tend towards positive commons

Why "unfortunately" ??

 

PNP circuits did, unfortunately, tend towards positive commons.

Typical electron-over-hole bias.

ak

 

Just for the heck of it I looked up the 2N404. I didn't think they made germanium transistors anymore. The RadioShack parts use something like a 2SC number. Which were also germanium as I recall.